Melt butter in sauté pan. Add onion and sauté until translucent.
Add tomato and spinach; sauté until wilted. Add fiddleheads, salt and pepper. Toss until incorporated and warmed through.
Assemble dish: place biscuit halves open-faced on a plate and mound vegetable mixture on top of each. Place a poached egg on top of vegetables. Drizzle hollandaise sauce over entire dish and garnish with salt, cracked pepper and chives.